Why doesn't :nth-child() work?

Question

Layout

I don't know why, but I can't access the nested div's children with :nth-child().

<div class="post_right-section">
                            <h5>18 oct</h5>
                            <div>
                                <h3>Startup ideas need to be funded</h3>
                                <p>By Khalil Uddin in Development</p>
                                <p>
                                    Lorem ipsum dolor sit amet, consetetur sadipscing elitr, 
                                    sed diam nonumy eirmod teduntlabore et dolore magna aliquyam 
                                    erat, sed diam voluptua. At vero eos et accusam et justo duo 
                                    dolores et erebum. Stet clita kasd gubergren, no sea takimata 
                                    sanctus est Lorem ipsum dolor sit am Lorem ipsum dolor sit 
                                    amet, consetetur sadipscing elitr, sed diam nonumy eirmod 
                                    tempor invidulabore et dolore aliquyam erat, sed diam
                                </p>
                                <button>Read more</button>
                            </div>
</div>

div.post_right-section div:nth-child(1){
    font-size: 50px;
}

Answer 1

:nth-child() - Locates one or more elements based on their position among a group of adjacent elements. Those. the original selector says we're changing the font-size to 50px on the element that's div at position 1 , but we have an h3 element at position 1 .
You need :nth-of-type()